This invention relates to improvements in scanning x-ray apparatus capable of performing both x-ray diffraction and x-ray fluorescence spectroscopy.
Numerous x-ray apparatuses capable of performing both x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy are well known in the x-ray art. For simplicity, apparatus of this type is referred to herein as "XRD-XRF" apparatus.
In general, XRD-XRF apparatus comprises (A) a gonimeter having a first rotatable platform and (B) means supported by the platform for holding the specimen in a position intersected by the axis of rotation of said first rotatable platform. Also included are (C) means for generating X-rays, (D) a source collimator for collimating the generated X-rays and beig so disposed that the collimated X-rays are incident on the specimen in the direction of the axis of said collimator, and (E) detecting means for detecting X-rays reflected from said specimen in response to incidence thereon of said collimated rays, said detecting means terminating at one end thereof in a snout for introducing the reflected X-rays into the detecting means.
Also included is (F) a wave-dispersive or energy-dispersive analyzer disposed near the entry end of said snout and operably associated with said detecting means for analyzing both X-ray fluorescent emission and absorption spectra and X-ray diffraction patterns generated by incidence of said collimated rays on said specimen.
Further included are, (G) first rotating means for rotating said specimen holder such that the specimen rotates relative to the incident X-rays (collimator axis) to a variable angular displacement in the plane containing the collimator axis and perpendicular to said axis of rotation, and (H) means operable in conjunction with such rotation of said specimen holder for concurrently rotating said detector such that said snout rotates relative to said collimator axis to a variable angular displacement 2.theta. in said plane such that for each value of displacement .theta. the value of 2.theta. displacement is substantially double that of displacement .theta..
An example of a well known x-ray apparatus encompassed by the above description is the XRD-6 Diffractometer introduced commercially by General Electric Company and now commercially available from the Diana Corporation (West Haven, Connecticut and Woburn, Massachusetts). The sales and technical brochures for the XRD-6 Diffractometer are incorporated herein by reference.
It has been heretofore known, in principle, that x-ray analysis and especially x-ray fluorescent spectrometry can be enhanced by employing a vacuum chamber for the x-ray path. See generally Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd ed. (1968), vol. 22, pages 438-467 and the Jenkins article "Interdependence of X-Ray Diffraction and X-Ray Fluorescence Data" in Advances in X-Ray Analysis, edited by Barrett et al., vol. 21, pages 7-21. In FIG. 6 at page 20 of the referenced article, Jenkins shows a diagram of an energy dispersive spectrometer/diffractometer combination and states a disadvantage of that apparatus as "A disadvantage with this configuration is the difficulty in completely removing air from the path of the fluorescence emission and, as a result, only characteristic lines down to S(Z=16) can be measured."
The prior art attempts to enhance the quality of x-ray analysis by incorporating x-ray path vacuum chambers into XRD-XRF apparatus of the Jenkins and other configurations have not been entirely satisfactory from the standpoint of measurability of characteristic lines of light elements, i.e. elements having atomic numbers (Z) below 16.
Briefly stated, it has unexpectedly now been found, by practice of the present invention, that the sensitivity of XRD-XRF apparatus for elements having atomic no. below 16 can be substantially increased by use of an environmentally controllable three-cylinder x-ray path chamber in combination with such apparatus. Use of the chamber (described in greater detail below) has surprisingly been found to sufficiently increase the sensitivity so that element-identifying or characteristic lines of elements having atomic numbers at lest as low as 10 can be measured by the improved XRD-XRF apparatus of this invention.